Method and device for heat treatment of metals

ABSTRACT

A furnace and resultant novel method for the heat treatment of metal parts, particularly of alloys containing titanium, comprising a heated retort maintained under continuous pressure by an inert gas with the retort feeding directly into a liquid quench bath. The parts are admitted to the furnace through a vacuum trap so that no air can enter the furnace to contaminate the material.

United States Patent Inventor Appl. No,

Filed Patented Assignee Harlan G. Gear-hart La Canada, Calif. 732,796

May 6, 1968 May 25, 1971 VST Corporation Pasadena, Calif.

METHOD AND DEVICE FOR HEAT TREATMENT OF METALS 6 Claims, 1 Drawing Fig.

US. Cl 266/4R,

148/13, 148/133 lnt.Cl C2ld1/66 Field of Search 266/4, 4 A,

VACUU M PUMP References Cited UNITED STATES PATENTS 6/1908 Thompson 266/4 6/1908 Thompson 266/4 3/1948 Loux 266/4 4/1967 Garwood et a1. 148/13 Primary Examiner-Gerald A. Dost Attorney-Sokoloski and Wohlgemuth ABSTRACT: A furnace and resultant novel method for the heat treatment of metal parts, particularly of alloys containing titanium, comprising a heated retort maintained under continuous pressure by an inert gas with the retort feeding directly into a liquid quench bath. The parts are admitted to the furnace through a vacuum trap so that no air can enter the furnace to contaminate the material.

METHOD AND DEVICE FOR HEAT TREATMENT OF METALS Parts formed of titanium alloys require a final heat treatment in order to obtain desired high strength properties. At the temperatures of the heat treat, normally from l700 to l750 F., the titanium alloy is extremely susceptible to contamination with oxygen. To date, attempts to prevent the contamination from occurring during the pressure from treatment have generally not met with much success. Thus, the outer contaminated layer must be machined off the part after the heat treatment, which further increases, to a considerable degree, the cost as well as time expended in forming titanium parts.

In order to prevent contamination, attempts have been made to heat treat the titanium parts in a furnace under an inert atmosphere. Typically, the prior art continuous furnaces contain a conventional shaker bed for advancing the parts through the heated region of the furnace. An inert gas such as argon is forced into the furnace under pressure from a separate source. The parts are fed onto the shaker through an opening provided in the furnace, which opening additionally serves as a bleedoff for the argon in an attempt to prevent the atmosphere from entering. Normally, a second bleedoff is provided in the furnace to assure significant pressure of the argon therein. The parts then drop off the shaker into a liquid quench. The quench extends into a portion of the furnace and a pocket of stagnant atmosphere and vapor from the quench remains at this point. Even in this prior art furnace, the air is not completely prevented from being admitted to the heating chamber, and thus some contamination of the parts results. In addition, many prior furnaces attempt to overcome the contamination problem by heat treating on a batch basis in a sealed furnace. This, however, results in a longer processing time and the parts are subjected to atmosphere when they are conveyed to the quench. Additionally, a very slow quench is obtained from the batch quench. It has been found that it is imperative, in order to prevent contamination, that the parts go directly from the heat treatment portion of the furnace into the water quench without contacting any oxygen.

Thus it is an object of this invention to provide a device for the heat treatment of metal parts, particularly those containing titanium, which will direct the parts from the heat treatment section directly to a water quench without contamination of air.

A further object of this invention is to provide a device for the heat treatment of metal parts, particularly those containing titanium, where the parts are admitted to the heated portion of the device without the possibility of air contaminant entering with the part.

One further object of this invention is to provide a novel method for the heat treatment of metal parts, particularly those including titanium, which prevents the possibility of contamination of the parts from air.

The above and other objects are accomplished by the device and method of this invention comprised of a metal retort which is pressurized with a gas such as argon. The retort has disposed therein a conventional shaker bed for moving the parts from one end to the other. Alternatively, a continuous belt can be utilized for this purpose. A hopper feeds the parts to be heat treated to one cooled end of the retort, dropping the parts onto the shaker bed. Prior'to entering the retort, the parts pass through a vacuum trap which is comprised of a section of pipe between the hopper and the retort, having a vacuum valve on each side thereof. The vacuum valve adjacent the hopper opens to admit the parts to the section, while the downstream valve adjacent the retort is closed. The upper valve adjacent the hopper is then closed and a vacuum drawn on this section. After the vacuum is drawn removing the air contaminant, the section is filled with argon and the downstream valve is opened letting the parts drop onto the shaker. Heating coils surround the retort downstream from the cooled entry portion and heat the parts to the desired temperature as they are moved along the shaker bed. The parts drop off of the shaker bed through a downspout portion of the retort which passes into and below the surface'of a quenching bath of water or the like. The depth of the spout in the water determines the pressure of argon gas needed to be maintained in the retort. For example, if the spout is 15 inches below the surface of the water, then the pressure of the argon must be sufficient to prevent the water from entering the spout and must be equivalent to 15 inches of water. As can be seen, the water thus serves to seal the outlet portion of the retort and prevent contamination from entering. The parts after leaving the downspout portion of the retort drop onto a continuous conveyor belt which carries them out of the water quench.

It is believed the invention will be better understood from the following detailed description and drawings in which:

The FIGURE is a partially sectioned schematic representation of the device of this invention.

Turning now to the Figure, the device 11 of the invention comprises a cylindrical retort 13, preferably of a metal such as an lnconel alloy which can sustain the high heat treat temperatures required. A hopper 15 is provided adjacent one end of the retort 13 for feeding the parts thereto. The hopper feeds directly to a vacuum trap section 17 which is formed of a cylindrical housing 19, which is part of an inlet line 20. Adjacent the bottom of the hopper, at the top of the vacuum trap 17 is a first conventional vacuum valve 21. A second vacuum valve 23 is located at the bottom of the trap 17 toward the retort. The vacuum valves 21 and 23 are of conventional construction and can, for example, be normal vacuum gate type valves. Such valves can be, of course, manually or automatically actuated.

lntersecting the vacuum trap section 17 is a vacuum line 25 connected through valve 27 to a conventional vacuum pump 29. Additionally, a vacuum line 31 connected through valve 33 is directed to the retort 13 for drawing a vacuum therein. Also intersecting the vacuum trap section 17 is a line 35 connected through valve 37 to line 39 which serves to direct a pressurized gas from container 41 to the vacuum trap section. Line 39 additionally passes directly into the retort 13 for conducting the pressurized gas thereto. A pressure regulator 43 and flow scope 45 are in line 39 to control the pressure of the gas from source 41 and observe the flow rate respectively.

Cooling coils 47 surround the portion of the retort adjacent the inlet 49 from the vacuum trap and hopper and extend for a portion of the retort to prevent the heat from affecting valves 21 and 23. Disposed in the retort is a conventional shaker bed 51 having raised sides 53 to prevent the parts dropped from hopper 15 from falling off. Shaker beds are made by various companies including American Gas Furnace Co., and C. l. Hays Co. The shaker bed is actuated by a shaker 55 disposed outside of the retort at the front end thereof. The connection between the shaker 55 and the bed 51 is through the front wall 57 of the retort and can be sealed by means of conventional O- ring seal arrangement 59 or its equivalent. Shaker beds are quite old in the art and are conventionally used in heat treat furnaces for advancing parts therethrough. Any of such conventional shaker beds can be utilized as long as precaution is taken to adequately s'ealthe shaker mechanism such as shown at 55 schematically to prevent leakage of air into the retort. Alternative to the shaker bed a conveyor belt can be utilized.

Downstream form the cooling coils 47 and surrounding the retort are resistive heating coils 61. The heating coils are enclosed by a steel jacket 63 and brick insulation 65 in a conventional arrangement. The heating coils serve to heat the retort in that region to a heat treat temperature desired and can be controlled by conventional rheostat or other means.

The retort is provided with a downwardly directing spout portion 67 at the end opposite from the entrance hopper end. The shaker bed terminates at a point over the spout portion 67 such that the parts drop off of the shaker and through the spout. Below the spout is disposed a container 69 for the liquid 72 utilized to quench the parts that have been heat treated The spout extends a given depth, a, below the surface of the liquid material. The bottom opening of the spout can be sealed by a door 71 actuated through a valve mechanism 73. in a fully opened position, as seen in the Figure, the door 71 is angularly disposed relative to the spout so that the parts can be directed onto a conveyor belt 77 located in the bath for carrying the parts to a suitable drying means.

To explain the sequence of operation of the device and thus the method herein involved, reference is again had to the Figure. To initially start up the apparatus, the door 71 is closed and sealed tight against the bottom of the outlet spout 67 of the retort. All of the valves in the system are closed with the exception of the valve 33. The vacuum pump is then started, drawing the atmosphere out of the retort 13 through line 31, thus purging the device. Valve 33 is then shut and the pressure regulator 43 from the source 41 of argon is opened to admit the argon to the retort through line 39. The pressure is regulated to be sufficient to provide enough pressure to lower the head of water 72 in the tank 69 a distance ofa" so that it does not come into the spout 67. As indicated, for example, if the spout extends 15 inches below the surface of the water, a pressure of argon equal to l inches of water is required in the retort.

Concurrently with the start of the flow of the argon, the coolant is circulated in the coils 47 and the heater elements 61 are activated and the retort is brought to operating temperature. Parts are then fed to hopper 15 and the vacuum valve 21 is opened admitting a selected number of parts to the vacuum trap 17, whereupon the valve 21 is subsequently closed. After the parts are disposed in vacuum trap 17, valve 27 is opened and the vacuum pump 29 will draw the air from the trap 17 through line 25 to create a vacuum therein on the order of about microns. As is apparent, this serves to completely remove the contaminating air or oxygen surrounding the parts so that none will be admitted to the retort. A pressure gauge 75 can be provided and electronically connected to valve 37 through a solenoid, not shown, whereupon the valve 37 is opened when the desired vacuum level is reached in trap 17. The opening of valve 37 then allows the argon to enter the trap 17 through line 35 enabling an equalization of pressure on either side of the valve 23. After the argon has been admitted to the trap 17, valve 23 is opened. Once again, valve 23 can be made to be electronically responsive to the gauge 75 opening when the pressure determined by the gauge is equal to the pressure in the retort. The opening of valve 23 then allows the parts to drop on the the shaker bed 51. The shaker bed 51, or a moving belt, is designed to advance the parts along the retort so that they will remain at the heat treat temperature region of, for example, l700- 1 750 F. for titanium alloys, for residency time of about l0 to minutes. The parts then fall off the end of the shaker bed through spout 67 striking door 71 prior to falling onto the conveyor belt 77 and the water quench. As has been previously indicated, the door 71 is angularly disposed relative to the bottom of the spout. This serves not only to direct the parts onto the conveyor belt but additionally to prevent to a degree rising steam form attempting to come up into the spout 67. Obviously, when the hot metal parts strike the water, steam will be created and bubbles thereof will attempt to rise to the surface of the bath.

It should be pointed out that not only is the pressure of gas in the retort maintained to prevent the liquid quench from entering, but the gas is flowed atdesired continuous rate. By having such a continuous flow of gas, any contaminants that might enter from the quench bath are swept back into the bath, or are, in fact, prevented from flowing up into the retort.

Though the invention has been described with particular relation to titanium alloys, it should be apparent that any metal alloys can be heat treated in accord with this invention. The temperatures of heat treat, the gas in the retort and the liquid quench can all be varied within the scope of the invention to accommodate other materials.

lclaim:

l. A device for heat treating metals in a controlled atmosphere, comprising:

a heated retort,

means adjacent one end of said retort for admitting the metal to said retort, said means including a vacuum trap, means for advancing said metal through said retort toward the opposite end thereof,

a downwardly directed spout at said opposite end for conducting said metal below the surface of a liquid quenching bath,

and means for placing said retort under an inert gas pressure sufficient to prevent liquid in the quenching bath from entering said spout.

2. The device of claim 1 wherein said means for admitting metal to said retort comprises:

an inlet line,

two spaced-apart vacuum valves disposed in said line forming a vacuum trap chamber therebetween.

3. The device of claim 2 further comprising;

means for drawing a vacuum on said vacuum trap chamber.

4. The device of claim 3 additionally comprising means for admitting an inert gas atmosphere to said vacuum trap chamber.

5. The device of claim 1 further comprising:

means for closing the outlet of said spout, and means for selectively drawing a vacuum on said retort.

6. The device of claim 1 further comprising:

a liquid quench bath disposed about a portion of said spout.

3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,580,555 Dated June 25, 1971 Inventor(s) rlan G. Gearhart It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

IN THE HEADING Column 1, line 6, correct:

"VST" to -VSI--.

IN THE SPECIFICATION Column 1, line 8, correct:

"pressure from" to -heat.

Column 2, line 61, correct:

"form" to -from.

Column 3, line 43, delete the second occurrence of "the" and insert therefor -to-.

Column 4, line 4 correct:

"form" to -from-.

Signed and sealed this 26th day of October 1971 (SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attestlng Officer Acting Commissioner of Patents 

2. The device of claim 1 wherein said means for admitting metal to said retort comprises: an inlet line, two spaced-apart vacuum valves disposed in said line forming a vacuum trap chamber therebetween.
 3. The device of claim 2 further comprising: means for drawing a vacuum on said vacuum trap chamber.
 4. The device of claim 3 additionally comprising means for admitting an inert gas atmosphere to said vacuum trap chamber.
 5. The device of claim 1 further comprising: means for closing the outlet of said spout, and means for selectively drawing a vacuum on said retort.
 6. The device of claim 1 further comprising: a liquid quench bath disposed about a portion of said spout. 